1. Field of the Invention
The present invention relates to a float valve device suited for a fuel cutoff valve for preventing a fuel from flowing out of the fuel tank of an automobile when the liquid level of the fuel tank rises.
2. Description of the Related Art
In Japanese Patent No. 3,257,437, for example, a fuel cutoff valve of the kind used in related art systems is disclosed. The fuel cutoff valve includes: a case body forming a valve chamber connected to a communication passage for establishing communication of the inside of a fuel tank with the outside; and a float valve member accommodated in the valve chamber and having a closed portion at its upper portion for opening/closing the communication passage so that it may move upward and downward by increasing/decreasing a buoyancy with a liquid fuel in the fuel tank to flow into and out of the valve chamber thereby to open/close the communication passage with the closed portion. The fuel cutoff valve is characterized in that the float valve member includes: a cylindrical float body forming a float chamber; a guide portion having a plurality of fins projecting vertically from the outer side wall portion of the float body and arranged and spaced from each other in the circumferential direction of the float body so that the float body is vertically guided by the individual sliding movements of the ridge portions of the fins on the inner side wall face of the valve chamber; communication passages formed individually between the fins for aerating the upper and lower spaces of the valve chamber partitioned by the float body; and a throttle forming step portion projecting from the outer side wall portion of the float body and between the fins for narrowing a portion of the communication passage.
In JP-A-8-225022, on the other hand, there is disclosed a liquid cutoff valve. This liquid cutoff valve includes: a hollow valve body disposed above a liquid reserving tank; a valve member inserted in the hollow inside of the valve body for moving upward and downward with the level of the tank liquid to flow into the valve body; a passage opened in the upper portion of the valve body for establishing the communication between the inside and outside of the tank; and a valve seat disposed at the opening portion of the passage. The valve member includes: a float; and a valve disc so held above the float as to move relative to the float and having a valve portion, so that the valve portion of the valve disc forming the valve member comes into and out of contact with the valve seat in accordance with the height of the level of the liquid to flow into the valve body, thereby to open/close the passage. The liquid cutoff valve is characterized: in that the valve disc is so held above the float as to be inclined with a plurality of pawls, one of which is shorter than the remaining pawls; and in that on the opposite side of the shorter pawl with respect to the center of the valve seat, there is disposed a projecting portion, against which the upper face of the valve disc is brought into abutment at the valve opening time by the upper portion of the valve body. In this liquid cutoff valve, moreover, rotation stop means for stopping the float relative to the valve body is constructed by forming vertically extending recesses in the side wall of the float and by forming projections on the inner circumference of the valve body for being fitted in the recesses.
In the fuel cutoff valve disclosed in Japanese Patent No. 3,257,437, the fins are vertically projected from the outer circumference of the float body and arranged in parallel at a predetermined spacing so that their ridges may individually slide on the inner wall face of the valve chamber thereby to act as vertical movement guide portions. However, the fuel cutoff valve is not provided with the rotation stop means for stopping the rotation of the float body relative to the case body.
On the other hand, the liquid cutoff valve disclosed in JP-A-8-225022 is provided with the rotation stop means for stopping the rotation of the float relative to the valve body by forming vertically extending recesses in the side wall of the float and by forming projections on the inner circumference of the valve body for being fitted in the recesses. However, this rotation stop means is provided for preventing the interference between the projections disposed on the upper portion of the valve body and the pawls disposed at the upper portion of the float.
On the other hand, those float valve devices are generally manufactured by injection-molding a synthetic resin. Moreover, these float valve devices are closed when the crest portion formed on the upper portion of the float valve member is fitted in close contact with the communication hole formed in the upper wall or partition of the valve case. However, there is such a tendency that the outer circumference of the crest portion of the float valve member or the inner circumference of the communication hole of the valve case may be deformed from the designed round shape in a predetermined direction in dependence upon the gate position at the injection molding time.
However, no consideration has heretofore been taken into those deformations depending upon the gate position. This has raised a problem that the insufficient roundness forms a clearance between the sealing faces thereby to cause a leakage of the liquid.